In the known refrigerating systems, the operation of the hermetic compressor is obtained by driving a single phase induction motor through electromechanical control devices. In these systems, the operative and stop periods of the compressor are defined as a function of a temperature, which is detected by appropriate sensors located inside the refrigerating cabinet of refrigerators and freezers in which said refrigerating system is applied. The compressor stop occurs whenever the temperature inside the cabinet is within a predetermined temperature interval. These systems are also provided with starting and thermal protecting devices for the hermetic compressors, usually consisting of electromechanical devices, due to their strength and simplicity.
A disadvantage in the presently used systems is in the amount of different electrical and electromechanical devices that are employed in the hermetic compressors and that have redundant functions, thereby also requiring individual connections and calibration. Said devices also generate noise and electromagnetic interference, since they are provided with movable contacts.
Another disadvantage in the present systems is the insensibility to the supply voltage variations, which impairs the function of thermal protection, resulting in overloading more severely the insulating material of the motor, and the possible overall malfunctioning of said motor in extreme voltage conditions. Moreover, for carrying out other functions differing from those cited above, the refrigerating systems require the use of additional peripheral devices, which mean a larger number of components and electrical connections, thereby increasing the cost of the assembly and allowing the occurrance of failures in said connections and components.